This application relates generally to ink xerography and printing, and/or ink jet printing. Various embodiments disclosed herein are directed to methods and apparatus for reducing imaging artifacts known as halos in color copiers. For example, ink pile height may be adjusted in color xerographic images through image processing ink coverage reduction methods.
Color images are commonly represented as one or more separations, each separation comprising a set of color density signals for a single primary, secondary, tertiary or multiple colors. The color density signals are commonly represented as digital gray or contone inks, varying in magnitude from a minimum to a maximum, with a number of gradations between, corresponding to the bit density of the system. For example, a common 8-bit system provides 256 shades of each separation color. A color of ink can therefore be considered the combination of intensity of each color separation for that ink, which when viewed together, present a combination color. Usually, printer signals include three primary colors cyan (C), magenta (M) and yellow (Y) signals and a black (K) signal, which collectively can be considered the printer color signals. Each color signal corresponds to a separation, and when combined together with the signals corresponding to the other separations forms the color image. For printing, each separation causes a layer of toner to be deposited on a toner receiving substrate. The combined layers form the color image.
Multi-color electrophotographic printing machines which use multi-colored toners are substantially identical in each color image forming process to the process of black-and-white printing, which uses only black toner. However, rather than forming a single latent image on the photoconductive surface, several single color latent images corresponding to color-separated images of the original document are recorded on the photoconductive surface. Each single color electrostatic latent image is developed with toner particles of the corresponding color. This process may be performed in a single pass, or in multiple passes during which image formation is repeated a plurality of cycles for differently colored images using their respective corresponding colored toner particles to form color toner images. Each single color toner powder image is transferred to a copy sheet in superimposed registration with the other toner powder images. Alternatively, there can be an intermediate transfer that takes place on a surface other than the paper (copy sheet), and subsequently transferred to the copy sheet in a second transfer.
This creates a composite multi-layered toner powder image on the copy sheet. The copy sheet is separated from the photoconductive member or intermediate transfer surface and, thereafter, the multi-layered toner powder image on the sheet is fed through a fusing apparatus and permanently affixed to the copy sheet, thus creating a multi-color document. In a black and white or multi-color electrophotographic printing machine, the copy sheet is typically brought into moving contact with the photoconductive member or intermediate transfer surface during toner powder image transfer to the copy sheet. A sheet transport apparatus is typically provided for receiving the copy sheet continuously as it is incrementally separated from the photoconductive member, and for transporting the copy sheet towards and into the fusing apparatus.
In recent years, so-called preflight softwares have been developed. Such applications test print submissions for features that may cause possible defects (e.g., missing fonts, inappropriate raster image resolution, use of spot colors on a process color device, color spaces, and the like). Often users may select from among hundreds of possible criteria. Preflight software packages now form an established part of the printing industry and include offerings from a range of vendors.
Contone raster images in, for example, a CMYK print engine's color space, use multiple bits per ink to represent their output. Formats may vary, but very commonly eight bits are used to represent each color. Hence, for a CMYK raster image including four colors (cyan, magenta, yellow and black), 32 bits are used to represent each ink. In general, a contone raster image can become device-dependent when a color decomposer converts an output that is targeted for a CMYK printer to the CMYK color space, during which process any current rendering information is applied. The resulting decomposer output files then contain the CMYK data needed to target a specific output device. Examples of contone raster image files include TIFF 6.0 Technical Note #2 files, and contone raster images stored in Portable Document Format (PDF) files by a JPEG compression algorithm. The above-described examples of raster image files may also be contained in Page Description Language (PDL) files. Examples of PDLs include Adobe Postscript, Adobe Portable Document Format (PDF) and Hewlett Packard's Page Composition Language (PCL).